Adaptation of Candida albicans to growth on sorbose via monosomy of chromosome 5 accompanied by duplication of another chromosome carrying a gene responsible for sorbose utilization.

Candida albicans, a fungus that normally inhabits the digestive tract and other mucosal surfaces, can become a pathogen in immunocompromised individuals, causing severe or even fatal infection. Mechanisms by which C. albicans can evade commonly used antifungal agents are not fully understood. We are studying a model system involving growth of C. albicans on toxic sugar sorbose, which represses synthesis of cell wall glucan and, as a result, kills fungi in a manner similar to drugs from the echinocandins class. Adaptation to sorbose occurs predominantly due to reversible loss of one homolog of chromosome 5 (Ch5), which results in upregulation of the metabolic gene SOU1 (SOrbose Utilization) on Ch4. Here, we show that growth on sorbose due to Ch5 monosomy can involve a facultative trisomy of a hybrid Ch4/7 that serves to increase copy number of the SOU1 gene. This shows that control of expression of SOU1 can involve multiple mechanisms; in this case, negative regulation and increase in gene copy number operating simultaneously in cell.